Glen Whitman has been compiling a list of The Two Things: pithy wisdom summing up the core of any subject in two items. Some are honest attempts at encapsulating a topic:
The Two Things about Project Management:
1. The schedule will slip.
2. It's about how you manage the schedule slippage.
The Two Things about History:
1. Everything has earlier antecedents.
2. Sources lie, but they're all we have.
Some have a grain of truth but are mostly just funny:
The Two Things about Binary Systems:
The Two Things about Web programming (as it is mostly done in the real world):